Watch an Oil Painting Instantly Lose 200 Years of Grimy Varnish

Fine art is often coated with varnish for the same reason furniture is: it provides a protective barrier to the elements. But varnish turns yellow over time, and an even less attractive color after a few centuries—which is why art restoration experts need to strip old varnish off and reapply it when a painting becomes unsightly. In a Twitter video posted by Philip Mould on Monday, the art dealer and Fake or Fortune? host showed just how dramatic this transformation can be:

How a restorationist manages to scrub off the varnish without also erasing a priceless work of art is a mixture of skill and trade secrets. One method involves two pieces of cotton, one soaked in a solvent like turpentine, the other in a neutralizing liquid that stops the turpentine from eating straight through the canvas.

But whatever substance Mould applied to this Jacobean portrait is way too thick to be plain turpentine. We’ve reached out for more information on what set of chemicals made this miraculous restoration possible: